This invention relates to a radio base station for use in a mobile digital communication system and, in particular, to a method of detecting interference in a control channel.
As well known in the art, the mobile digital communication system comprises a plurality of mobile stations sprinkled over a zone, a radio base station, and a radio exchange station. The radio base station is connected to the mobile stations via a control channel and a plurality of speech channels. The radio base station carries out radio communication to the mobile stations. More specifically, the radio base station sets a particular one of the speech channels for each mobile station to carry out a transmission of a communication signal via the particular speech channel. After the particular speech channel is set, the radio exchange station carries out an exchange connection for a desired subscriber.
A control signal for an outgoing call or an incoming call is transferred between the radio base station and the mobile stations via the control channel. The radio exchange station carries out control of the control signal. That is, the radio exchange station carries out, through the control channel, designation of free channels in the speech channels, outgoing/incoming call, exchange operation for a communication destination and so on. Inasmuch as a transferring time interval for the control signal is usually equal to a time interval of about 10 milliseconds in a digital exchange, there is very few opportunities for collisions although outgoing/incoming calls for the mobile stations are congested. However, when the radio base station receives via the control channel an interference electric wave having a relatively longer time interval extremely more than 10 milliseconds due to an external electric wave except for the mobile stations, it is feared that normal communication of the control signal is interfered.